Safety devices for sheet metal presses and the like



Oct. 21, 1969 E. R. N. JACKSON 3,473,357

SAFETY DEVICES FOR SHEET METAL PRESSES AND THE LIKE Filed Nov. 13, 19s? 3 Sheets-Sheet 1 By M'FJW A llorneys Oct. 21, 1969 E. R. N. JACKSON 3,473,357

SAFETY DEVICES FOR SHEET METAL PRESSES AND THE LIKE Filed Nov. 13, 196'? 3 Sheets-Sheet 2 Inventor fin/104:7 e /l e/Acmsan/ 83gb; r

Attorneys Oct. 21, 1969 E. R. N. JACKSON 3,473,357

SAFETY DEVICES FOR SHEET METAL PRESSES AND THE LIKE Filed Nov. 13, 1967 5 Sheets-Sheet 5 Q I@ M v Invcnlor ELIZABETH R.N. JACKSON By 9"? W" I Allorney United States Patent 3,473,357 SAFETY DEVICES FOR SHEET METAL PRESSES AND THE LIKE Elizabeth Rosemary Norton Jackson, Blaen Ochran, Llanellen, Abergavenny, Monmouthshire, England Filed Nov. 13, 1967, Ser. No. 682,073 Claims priority, application Great Britain, Nov. 18, 1966, 51,717/ 66 Int. Cl. B2141 55/00 US. Cl. 72-2 16 Claims ABSTRACT OF THE DISCLOSURE This invention relates to safety devices for sheet metal presses and the like, such as used, for example, in bending the edges of metal sheets.

In order to safeguard an operator from inadvertently moving his hand or arm beneath the press while in operation various expensive and cumbersome methods have been used to keep the operator out of reach of the tools. A guard is often provided and if this is close to the tools, on account of its cumbersome nature a restriction is imposed by it upon the types of tool which can be used in the press. Some guards are made of specific size to operate with a prearranged size of metal sheet, and are not therefore suitable for universal use. Moreover the use of guards generally tends to slow down production, and for these reasons guards are frequently swung to inoperative positions, and allowed to remain there even when a press is in operation.

The object of the present invention is to provide in a press safety means for protection of the operator, which will introduce little or no delay in the operational speed of the press.

With this end in view the invention consists in safety means for a sheet metal press or like machine comprising a contact-sensitive electrical conductive element insulated from the press frame, adapted to be located in a guarding position in front of a press, and adapted to be connected in an electrical control circuit by which operation of the press is controlled.

The electrical resistance element may be a conductive wire mounted in a frame, and the whole may be compact and light, allowing rapid movements, from positions of rest, as and when required. The arrangement may be such that if the conductive element is touched, e.g. by an operators hand, the resulting change of resistance activates the circuit in which the element is connected, and sets into operation automatic stop means, and/or warning devices, to prevent, or guard against, damage or injury. The conductive element may be raised and lowered between its fully closed, i.e. guarding, position, and its fully open position by mechanical connection with the ram of the press, or other suitable means, being closed just before the ram commences to move down in order to perform a pressing operation, and opened when the ram is completing a pressing operation, in order to alloW bending the plate.

The conductive element may remain open during, and after, completion of a pressing stroke in order to facilitate Patented Oct. 21, 1969 "ice withdrawal and infeed of workpieces, and to avoid possible damage to the element.

The invention will be clearly understood from the following description of one form (given, however, merely by way of example) which it may assume and this description will be more readily followed by reference to the accompanying drawings wherein FIGURES 1 and 2 represent somewhat diagrammatically, respectively in side elevation and plan, part of one form of safety means in accordance with the invention;

FIGURE 3 represents in side elevation a press illustrating how the safety means according to the invention may be associated therewith;

FIGURE 4 is the diagram of a control circuit to which the safety means shown in FIGURES 1-3 may be connected;

FIGURE 5 represents a micro-switch circuit which may be incorporated, and

FIGURE 6 represents in side elevation a modified form of press with which a guard in accordance with the invention may be used.

In carrying the invention into effect in one convenient manner, as shown in the aforesaid drawings, safety means for a sheet metal press may comprise a gate formed of two spaced vertical side channel members 1 of electrically conductive material between which extend wires 2 (or a single wire threaded zig-zag through holes in the channels). Each wire (or the single wire in zig-zag array) may be held near one end by a light spring (not shown) to draw it taut. Each channel 1 is mounted on a plate 3 of insulating material attached to a slide 4 which is vertically movable in a housing formed by a channel 5 with cover members 6. These housings are attached to spaced side plates 7 of the safety device.

The inner wall of each channel 5 is vertically slotted to accommodate a projecting T-shaped bracket member 8 attached to the slide 4. A lever 9 pivoted to a side plate 7 at 10 is connected to the bracket 8 by a pin-andslot coupling 11. When the slide 4- with its channel 1 is in its lowermost position the lever 9 is upwardly inclined in a rearward direction therefrom as seen in FIGURE 1.

The ram 12 of the press, (FIGURE 3) (to which is fitted a press tool 13) has attached thereto a rearwardly projecting bracket 14 (FIGURE 1) fitted with an adjustable, downwardly extending screw 15. A horizontal screw 16 fitted in the lever 9 a short distance rearwardly of the pivot 10, projects beneath the screw 15, with which it is aligned. As seen from FIGURE 1 a downward movement of the ram 12 and thus of the bracket 14 and pin 15 depresses the pin 16 and thus rocks the lever 9 to lift the gate 1, 2. Owing to the different spacings of the pins 11 and 16 in relation to the pivot 10 a substantial lift of the gate is caused by a comparatively small downward movement of the ram 12 and its pin 15. The lowermost position of the lever 9 and gate 1, 2 may be determined by an adjustable stop 17 towards which the lever may, if desired, be urged by a spring 18.

The movements of the gate during a pressing operation may be appreciated from consideration of FIGURE 3. For bending by the press a fiat metal plate may be rested on a base or anvil 19 in a substantially horizontal plane in which a substantial length of the plate will extend forwards from the press beneath the gate 1, which is in its raised, dotted line, position.

Just before the ram 12 descends the gate 1, falls, and thereafter when the ram 12 descends to press the tool 13 against the plate, the plate bends, and the forwardly projecting area swings upwards (FIGURE 3). In order to allow such swing the gate is raised by the action of the pin 15 on the lever 9, as described above, during the short final stage of downward movement of the tool 13. As a result the gate is lifted to the position shown in dotted lines in FIGURE 3.

A trip mechanism (not shown) may be provided to hold the gate 1, 2 in the uppermost position until just before the press cam reaches a top dead centre position, in order to enable a work piece to be removed after having been pressed, before the gate returns to its lowermost position. The gate is set so that in its lowermost position the lowest wire 2 is approximately A inch above the face of the bed or anvil 19.

In order that the wire(s) 2 of the gate shall serve as a safeguard against the risk of an operator putting in his hand beneath the press tool, the gate i.e. a channel member 1 is connected to an electric control circuit. The arrangement is such that when the selected resistance of the wire(s) 2 is in circuit, the circuit remains inoperative, but if the resistance is modified by contact, e.g. by being touched by an operators hand, the circuit is activated.

A convenient circuit which may be employed is represented in FIGURE 4 comprising a cascade array of transistors to which the gate can be connected at 20, arranged, when activated, to operate a relay 21 for stopping the press, cutting off power supply and/or actuating a warning or alarm.

The safety device may be attached to the end frame 22 of the press by bolts 23 engaging in slots 2- allowing fore and aft adjustment, in the side plates 7, and on the end frame 22 may be mounted a micro-switch 25 (connected between the gate 1, 2 and earth) adapted to be actuated by a projection 26 at the rear end of the lever 9 when near to its uppermost position. This micro-switch is depressed and open-circuited when the gate is lowered, but is closed, to short-circuit the gate to earth, when the gate is raised.

Referring to FIGURE a micro-switch may be fitted across terminals 31 and in a position where it is opencircuited by a cam (not shown) on the crank shaft of the press over an arc of rotation of about 120l40 from a top dead centre position, and the micro-switch is included in the gate circuit to render the gate operative only during the corresponding period of downward movement of the beam. Just before the tool 13 touches the metal sheet to be pressed the micro-switch is opened to isolate the electrical system of the gate so that should the work touch the gate the press will continue to operate until the electrical circuit is restored by closure of the micro-switch when the cam reaches a top dead centre position. The gate is lifted mechanically, or by any other means, after being isolated, and is held in this uppermost position until just before the cam reaches a top dead centre position. Should the gate fail to return to the lowermost position micro-switches 25 provided at the ends of the gate short circuit the gate wire 2 to earth and stop the press. The arrangement is such that any leak from the gate up to about megohms is effective to operate the relay and thus arrest the press. Leaks up to 25/30 megohms are effective if the earth potential shown in FIGURE 4 is increased to +9 volts.

Other circuits of greater sensitivity may be used, but care should be taken to ensure that they will not be affected by extraneous influences. The main control relay 27 (FIGURE 5) is connected to the contacts of the relay 21 by contacts 28, one of which has a neutral or earth connection 29. The contacts of relay 27 are connected by contacts 30, in series with contactors controlling the air valve and/or clutch/brake mechanism of the press. The contacts of relay 27 are also connected at 31 to the contacts of the micro-switch actuated by a cam on the crank shaft of the press, for isolating the electrical mechanism of the gate, as described above.

In FIGURE 6 is shown another form of press with which a guard in accordance with the invention may be used. The punch 32 cooperates with a pressure pad 33, which bears on a plunger 34 loaded by a spring 35. It

will be noted that a metal sheet 36 being worked is bent up by to come flat against the ram. Since the sensing wires 2 are very light the lifting means may consist of simple pneumatic pistons bolted to the ends of the press and having the wires directly coupled to the piston rods via insulating material. In such an arrangement the action of the pistons is controlled by an air valve operated by a cam on the main crank shaft of the press, or, in the case of a hydraulic press, by a valve in the downward pressure circuit.

From the above description it will be seen that the invention provides effective safety arrangements for metal sheet presses and like mechanisms, but it should be understood that the invention is not limited solely to the details of the form described above, which may be modified. in order to meet various conditions and requirements encountered, without departing from the scope of the invention.

What I claim is:

I. Safety means for a sheet metal press comprising an electric conductor supported in a guarding position in front of the press, but electrically insulated from the press frame, an electronic circuit and a source of electricity connected between said conductor and earth, in such a manner that no current flows through the said circuit and conductor unless and until said conductor is contacted by the press operator, and means for initiating arrest of said press, actuated by said electronic circuit when current flows therethrough as the result of contact by the operator with said conductor.

2. Safety means as claimed in claim 1 wherein the con ductor is slidable to and from its guard position.

3. Safety means as claimed in claim 1 wherein the conductor is reciprocable in a substantially vertical direction from and to its guard position.

4. Safety means as claimed in claim 1 wherein the conductor is formed of electrical wire mounted between rigid side members.

5. Safety means as claimed in claim 1 wherein the conductor is supported between slides mounted in guides or" a supporting frame.

6. Safety means as claimed in claim 1 wherein the conductor is mounted in a supporting frame provided with means for securing it to the frame of the press.

7. Safety means as claimed in claim 1 comprising a movable conductor and means operable by the press tool mechanism for moving the conductor.

8. Safety means as claimed in claim 1 comprising a movable conductor and means for moving the guard element including mechanical means actuated by contact therewith of the press tool mechanism.

9. Safety means as claimed in claim 1 comprising a movable conductor and means for moving said conductor. and wherein cooperating parts of the means for moving the conductor and the press tool mechanism are relatively adjustable to vary the extent of movement of the conductor effected by a given stroke of the press tool.

15. Safety means as claimed in claim 1 wherein the conductor is movable by a pivoted lever.

11. Safety means as claimed in claim 1 wherein the conductor is movable by a pivoted lever, and wherein Ll projecting member attached to the press tool ram rocks the pivoted lever when the ram approaches the lowermost limit of its stroke.

12. Safety means as claimed in claim 1 comprising means for retaining the conductor in open, non-guarding position until just before the press tool ram commences a downward pressure stroke.

13. Safety means as claimed in claim 1 wherein the conductor is connected by way of electrical amplifying means to a relay incorporating contacts connected in the operating circuit of the press tool.

I4. Safety means as claimed in claim 1 comprising .t

switch in the circuit incorporating the conductor adapted automatically to be open when the conductor is at or near to its closed, guarding position.

15. Safety means as claimed in claim 1 comprising in the circuit incorporating the conductor switch means operable by cam means associated with a main shaft of the press, to be open-circuited for part of each rotational cycle of the shaft, and to render the conductor operative only during a prearranged period of downward movement of the press.

16. Safety means as claimed in claim 1 wherein the References Cited UNITED STATES PATENTS 5/1941 MacMillin et a1. 83544 9/1965 Reinhold 83544 RONALD D. GREFE, Primary Examiner U.S. Cl. X.R. 

